Mechanism of sex: meaning, early studies, determinants, approaches


Mechanism of sex or sex motivation


Like in most primates, human males are more or less constantly potent and fertile.

Human females are, however, different from other mammals in that they have an increased capacity to experience orgasms and they lack estrus (a period of heightened sexual interest and attractiveness in females that usually coincides with their period of fertility).   It is suggested that evolution has given humans different ways of expressing sexual motivation, besides some specialized physical changes.

e.g. make-up, clothing, accessories, etc.

Morris suggests that the ability to experience orgasms in human females and the emotional involvement associated with sexual acts could be a way of strengthening the bond between the pair in our social setting.

Reproductive success is defined as passing one’s genes to the new generation.

This can be achieved directly (by having offspring), or indirectly (by nurturing and supporting the survival of the existing offspring). Whereas the direct method doesn’t harm human males, females use the indirect method, for which she seeks stability (economic and emotional).

Early studies mechanism of sex

  1. The first large-scale study of human behavior was carried out by Kinsey and his associates in 1938. The reports are a result of extensive interviews of 5300 male and 5940 women participants.
  2. H. Masters and V. E. Johnson studied human sexual behavior in the laboratory setup and have complied one of the most extensive and exhaustive findings on human sexual intercourse and orgasmic behaviors and patterns.

The Human Sexual Response Cycle

Masters and Johnson identified four distinct successive phases in the human sexual response cycle:

      1. Excitement Phase-   Fast excitement in response to any type of sexual stimulation (tactile, visual, auditory, olfactory stimulus, or fantasizing)
      2. Plateau Phase-  Receptivity to extraneous stimuli lessens and bodily sexual tension becomes intense
      3. Orgasmic Phase- Among women, there are significant inter-individual and intra-individual differences in the subjective experience of orgasms (in terms of intensity, duration and frequency). In males, the variation in the orgasmic reaction is very low.
      4. Resolution Phase- In males orgasm is followed by a refractory period in which arousal is reduced and sexual tension is reduced to the level of the excitement level. In women, there is a high level of tension following orgasm, and if stimulation continues, they can experience immediate and repeated orgasms. After orgasm, the resolution phase involves a more or less gradual reduction of sexual tension.

Gender Differences in Sexual Arousability

It is generally reported that human males have higher sexual arousability as compared to females. Different explanations have been put forth to explain this difference –

  • According to Kinsey, males have a greater capacity to be sexually conditioned as compared to females, and thus have higher arousability.

  This explanation was criticized by many.

Another explanation is that (at least during adolescence), males have a stronger “biologically roused tendency”  to become sexually aroused, as compared to females.

This could possibly be because of greater concentrations of androgens in males.

  • The third explanation is that learning experiences may be the factor that leads to gender differences in sexual arousability.

            According to this approach, males indulge very actively in masturbatory acts and fantasizing. This leads to several different stimuli being associated with sexual arousal in males.

Thus they can get easily aroused by many stimuli in the environment.

  • On the other hand, societal norms usually lead to females hardly indulging in such behaviors.

This relative sexual inactivity of adolescent females may prevent them from learning many things about how to be aroused and responsive.

Females may take more time to become free from sexual inhibitions, but to some extent, also to learn to become sexual.

Physiological Determinants of Arousal

I.  Hormonal Mechanisms

Sex hormones have two effects:

a) Activation effects (wherein they influence the ongoing sexual arousability of appropriate neural and muscualr structures).

b) Organizational effects (wherein they play a role in the development and organization of these structures).

The gonads (testes in males and ovaries in females), are relatively inactive in childhood.

At puberty, gonads are stimulated by gonadotropic hormones released from the pituitary gland.  This helps them to release their own hormones (androgen testosterone by testes in males and estrogen and progesterone by ovaries in females).


A. Hormonal Mechanisms – Activation Effects

In most species of mammals, the sexual receptivity of females is closely related to the estrus cycle, which is controlled by the ovarian hormones.

Ovariectomy abolishes the estrus cycle and sexual receptivity among them. They can be reinstated if ovarian hormones are administered artificially.   In monkeys the effects of ovariectomy are less prominent, and operated females may occasionally be receptive.

In humans, the effects of both ovariectomy and menopause are highly variable, with many women reporting no loss of sexual desire. Thus, arousability in women is not closely associated with levels of ovarian hormones. Evidence suggests that arousability in women is related to levels of androgens from the adrenal cortex.

In female cancer patients whose pituitary gland was removed, a marked decrease in sexual desire and behavior was observed.  This effect could be reversed with administration of androgens.

Increase and decrease in androgens also leads to increase and decrease in male sexual behavior.

Effects of Learning

Interestingly, experience alters the effects of castration in male dogs, cats, etc.

Rosenblatt found that testosterone injections reinstated sexual behavior in castrated male cats only if they were sexually experienced before castration.


B. Hormonal Mechanisms – Organization Effects

Characteristics of  Organizational Effects of Hormones:

    1. They occur during a critical period of special sensitivity before or around the time of birth.
    2. Their effects tend to be long-term and relatively permanent (although some researchers argue that they can be overcome by non-hormonal influences).
    3. Their effects may be delayed and become manifest only later in life.

These organizational effects explain how the small differences between males and females at conception can cause so many complex differences between males and females.

The X and Y chromosomes determine the hormonal status if the fetus, and the hormones organize its tissues in a masculine or feminine direction accordingly.


II.  Neural Mechanisms

Most aspects of the sexual response cycle are reflexes controlled by the spinal cord.

Spinal transaction does not disrupt sexual arousal behaviors, estrus cycle, and sexual behaviors in animals and humans. The destruction of cortical structures like the hypothalamus and the limbic system seems to have more severe negative effects on the copulatory pattern in males than in females.

The reason may be that neocortical regions play an important role in male sexual behaviors whereas hormonal mechanisms play an important role in female sexual behaviors.

The second explanation is that males play an active role in copulation and damage to higher brain region affects the functioning of complex behaviors (copulation being one of them).

  • Interaction Between Hormones and Neural Mechanisms

Prenatal Hormones:

Several studies have shown that male and female embryos  develop similarly during the early phases of gestation. If genetically female rats are injected with testosterone  during a particular period, they fail to develop normal female sexual behaviors in adulthood (even after administering estrogen and progesterone in adulthood).

Thus hormones, especially testosterone appears to enter body cells through the bloodstream and alters them in complex ways.

Even in humans, hormonal mechanisms influence psycho-sexual differentiation.

Developmental-Interactionistic Approach

However, in humans, social learning, upbringing etc. also play a very important role in sexual arousability, gender identity, sex-role behavior, and sexual orientation.


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